Earths magnetic field

[alias25]

I heard that the earths magnetic field changes every few thousands of years? is this true, if it is how does that happen

[Deeviant]

The earth's magnetic poles are in constant motion, moving in distances easily measured in just a year. This is the reason why magnetic compasses readings must be recalibrated over time.

I believe the best answer available today is that this is caused by some sort of shifting of the iron inside of earth.

[LURCH]

There is indeed geological evidence that the earth's magnetic field reverses periodically. The cause for the reversal is not really understood, neither the cause for the field itself. There is a thread about ithere (http://www.physicsforums.com/showthread.php?s=&postid=71398#post71398) .

The thread is largely based on the work of Dr. Daniel Lathrop of University of Maryland.Here is his website (http://complex.umd.edu/dynamo/index.html).